Electronic device and method for tracking energy consumption

ABSTRACT

The invention relates to an apparatus and method for tracking energy consumption. An energy tracking system comprises at least one switching element, at least one inductor and a control block to keep the output voltage at a pre-selected level. The switching elements are configured to apply the source of energy to the inductors. The control block compares the output voltage of the energy tracking system to a reference value and controls the switching of the switched elements in order to transfer energy for the primary voltage into a secondary voltage at the output of the energy tracking system. The electronic device further comprises an ON-time and OFF-time generator and an accumulator wherein the control block is coupled to receive a signal from the ON-time and OFF-time generator and generates switching signals for the at least one switching element in the form of ON-time pulses with a constant ON-time.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/868,130, filed Sep. 28, 2015, which is a continuation of U.S. patentapplication Ser. No. 13/788,941, filed Mar. 7, 2013, both areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to an electronic device and a method for trackingthe energy consumption, and more specifically to an electronic deviceand a method for determining energy consumption using the principle ofstoring energy in an inductor and transferring the energy into outputenergy storing components.

The present application relates to jointly owned U.S. Patent Applicationcorresponding to application Ser. No. 13/329,073 entitled, “ElectronicDevice and Method for Power Measurement.”

BACKGROUND

Reducing energy consumption is important in the development andimprovement of electronic devices, in particular if they are mobile orportable electronic devices. In order to save energy, electronic devicesare more and more controlled by sophisticated schemes in which themagnitude of the consumed currents varies over several decades ofmagnitude. In low power modes some hundreds of nA (nano-amperes) of acurrent may be consumed while other operation modes require up toseveral hundreds of mA (milli-amperes). It is often necessary to measurethese currents over a wide range (e.g. from nano-amperes tomilli-amperes) with an acceptable accuracy while at the same time beingable to track highly dynamic current changes. Furthermore, any sideeffects due to measuring the consumed energy should be avoided or wellcontrolled. For example, it is preferred that an increase of the energyconsumption due to the energy measurement itself not occur.

One of the most common techniques for measuring a current is ameasurement using a shunt device or a shunt resister. Using a shuntdevice for the power measurement requires very high precision analogueto digital converters in order to cover the full dynamic range of thepossible magnitudes of the currents. For example, when four and a halfdecades of measurement with one percent precision is required, a24-Bit-converter would be required. Furthermore, shunt devices generatea voltage drop. This voltage should be compensated, while thecompensation circuitry constitutes a potential source of errors. Directload compensation can be difficult. This means that the measurementrange and therefore the circuitry used for measuring the powerconsumption has to be adapted during the energy measurement procedure.This increases complexity and entails more potential errors.

Still further, measuring a current indirectly by measuring the voltageacross a shunt device requires an initial voltage change on the target.If a buffer capacitor is coupled to the target side (output side of anenergy transfer circuits), the buffer capacitor delivers currentimmediately and needs to be recharged. This behavior affects the truecurrent response of the device under test. Another approach of measuringthe energy consumption employs a current mirror. One side of the currentmirror delivers the current to the target including the targetcapacitor. The other side of the current mirror is coupled to an Amperemeter to which the mirrored current is fed. This approach has theadvantage that the distortion caused by the target capacitor isminimized. However, the required pairing of the power and sense fieldeffect transistors (FET) is rather poor and is not capable of trackingthe huge current magnitude to be supported.

SUMMARY

It is an object of the invention to provide an electronic device and amethod for measuring energy consumption in an energy consuming systemthat covers a large range of magnitudes of supply currents, high dynamiccurrent changes and does not affect the basic functionality of thecircuit which energy consumption is measured. According to an aspect ofthe invention, an electronic device is provided that comprises aswitched mode energy tracking circuitry. The switched mode circuitcomprises one of more switching elements, one or more in inductors and acompare circuit that controls the output voltage level to be at theselected voltage level. The switching element is configured to switch acurrent through the inductor and the switch may be a transistor. Thevoltage compare circuit may be an error amplifier, a voltage comparator,or an A/D converter which conversion result is compared to a referencedata. The control block is configured to control the ON-time andOFF-time of the switching element in order to transfer energy form aprimary energy source, e.g. power supply, to the output of the energytracking system and to control the level of the output voltage. Theelectronic device further comprises a control logic stage, errordetection and reporting block, and an accumulator of the individualON-time events.

The control logic stage generates the switching signals SW1 to SWi forthe switched transistors in the form of ON-time pulses with a constantON-time. The control logic state also controls the OFF-time which isused also as an indicator if the energy in the inductor is transferredto the output respectively of a capacitor. The voltage-compare circuitflags when the next ON-time pulse has to be generated. If the OFF-timeis not over before the next ON-time is triggered the system reports anerror condition. An error conditions is also reported if the outputvoltage VL is not within predefined limits.

The switching signals are formed according to a pulse density scheme.The highest density of pulses occurs when the On-time and OFF-time aremet at the time another ON-time is requested. Higher density is enabledby default or by control information e.g. a control bit and this ishandled by the control circuit as described previously. In an embodimentof the invention, the pulse accumulator can be in the simplestimplementation a digital counter. The counter in this embodiment is thenconfigured to count the number of ON-time pulses for determining theconsumed power based on the number of ON-time pulses per time. Theconstant pulse width of the ON-time pulses makes the influence of thesystem components such as the non-linear behavior of switchedtransistors or inductors negligible. The target voltage offset at theoutput of the energy tracking system is highly reduced. A wide range ofmagnitudes of the measured current can be covered.

According to another aspect of the invention, the electronic devicecomprises a first capacitor C1 coupled to the input of the energytracking system and a second capacitor C2 coupled to the output of theenergy tracking system. The ON-time of the switching element inconjunction with the inductor's value and the value of the capacitor C1is configured to keep the voltage within the system accuracyrequirements. The output capacitor C2 is of such value that the voltageincrease during transferring the energy from the inductor IND1 to INDiis within the accuracy expectations.

The energy tracking system of this embodiment is contrary to a pulsewidth modulation scheme and all energy in the inductor can betransferred to the output respectively to output capacitor C2. Thefrequency of the ON-time pulses is proportional to and practically alinear function of the consumed current. During a settled operationcondition, in which the input and output voltages and the charges on theinput and output capacitors have settled, each ON-time pulse of theswitched transfers about the same amount of the energy.

According to an embodiment of the invention, a reference impedance or areference resistor can be coupled to the output of the energy trackingsystem in order to make a reference energy measurement. The results ofthe reference measurement(s) can then be used for calibrating the systemto the energy consumption. Therefore, the number of the ON-time pulsescan be used for determining the energy consumption during normaloperation even with an unknown load. The unknown load according to anembodiment of the invention can be an electronic device.

In an embodiment of the invention, the electronic device comprises anenergy tracking system with a switching component, an inductor and atransfer support diode or switch. The switching component can then beconfigured to enable a current through the inductor and to stop furthercurrent flow from the input energy source, such as a power supply,battery etc. The voltage compare circuit can be an error comparator orerror amplifier. The voltage compare circuit is configured to send asignal to the control circuit and the ON-time generator so that theswitching component can be triggered or be prepared to be triggered. Theerror compare circuit serves to deliver the demand on energy to maintaina stable output voltage. The generation and frequency of the ON-timepulses can be controlled in response to a change of the output voltage.The ON-time pulses can be combined with a time stamp on an individualbasis or on a group of pulses.

Another embodiment of the invention includes ON-time pulses that arebased on a defined time and the difference to that defined time base isbounded by pulses or a group of pulses. The energy consumption may thenbe determined based on the number of the ON-time pulses per consideredtime period.

In an aspect of the invention, the energy consumption may then bederived from a phase variation of the ON-time pulses. This aspect allowsa quick evaluation of changes of the power consumption. The energytransfer during ON-time pulses usually is significantly smaller than theenergy stored on a first capacitor C1 coupled to the input of the energytransfer system. The energy withdrawn from the energy source at theinput of the energy transfer system influences the energy transferredduring the ON-time. The influence of the energy sourcing capability is afactor in the calibration cycle.

The energy stored on a second capacitor C2 coupled to the output of theenergy transfer system is also significantly larger than the energystored in the inductor during the ON-time and transferred to the outputand the capacitor C2 during OFF-time. The energy consumption may becalibrated by coupling one or more reference impedances to the output ofthe energy transfer system. The result of the calibration may then beused for normalizing the energy consumption during normal operation.During normal operation a target device or a device under test (DUT) isthen coupled to the output of the energy transfer system instead of thereference impedance. However, in another embodiment, the referenceimpedance may be coupled to the output while the target load device orDUT is still coupled to the output of the switched mode power converter.The energy of one or a group of ON-time pulses due to the additionalload of the reference load can be evaluated for calibrating the powermeasurement based on the energy pulse ON-time and OFF-time conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a circuit measuring the current, the voltage and the timingrelations to calculate the energy consumed within the load of thedevice-under-test.

PRIOR ART

FIG. 2 is a simplified circuit diagram of an embodiment of theinvention.

FIG. 3 is a diagram showing waveforms of signals of the circuit shown inFIG. 2 according to an embodiment of the invention.

FIG. 4 is a circuit diagram of an embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows a circuit 101 that measures the load current via avoltage-to-voltage converter 102, an A/D converter 104 and timer 106.The energy EL used by the load is calculated in block EL 108. Thevoltage VL is measured via the A/D converter 104. When the A/D converter104 is used for sequential conversions, phase related errors may occur.A timer 106 is used to create the time base t(b) for the A/D converter104. The energy EL used by the load (i.e. DUT) is calculated by theblock EL according to equation 1 below.EL=IL*VL*t(b)  Equation1

FIG. 2 shows a simplified diagram of an embodiment of the invention. Inthis embodiment, an energy tracking system 200 comprises energy transferblocks 202 and 204, a control circuit 201 and reference impedance 205.In this embodiment, each energy transfer block 202 and 204 comprises twoswitched transistors, a diode and an inductor. For example, energytransfer block 202 comprises switched transistors SW1 a and SW1 b, diodeD1, and inductor IND1. In this example two energy transfer blocks 202and 204 are shown. However, more than two energy transfer blocks may beused. Each inductor in an energy transfer block is coupled with one sideto a first switched transistor and with the other side of the inductorto an output of the energy transfer block. The switched transistors canbe referred to as energizing switches. The diodes may be replaced orcomplemented by a second switch. The control circuit 201 controls theenergy switches SWS1 a, SWS1 b, SWSia and SWSib. The control circuit 201will be explained in more detail later in the specification.

FIG. 3 shows the timing diagram for an energy transfer circuit that hastwo transfer paths. The first path has SW1 a, IND1, D1, and the ON-timesignal applied to SWS1 a. The second switch SWS1 b shown in energytransfer block 202, in this example, is not used. The second path (2=i)has SWia, INDi, Di, and the ON-time signal applied to SWSia. The secondswitch SWSib shown in energy transfer block 204, in this example, is notused. The two energy transfer paths are used mainly to enhance thedynamic range of delivering energy. The second switches SWS1B and SWSibare used (or switched in parallel) when the load conditions are higherthan the first path can serve. The system may have even more than 2paths enabling further spread of the dynamic range.

FIG. 4 shows more detail in the control circuit 201. The compare circuit406 is coupled to receive an external reference signal VL(ref) fordetermining a deviation of the output voltage VL. The output of thecompare circuit is coupled to the control logic stage CNTL1 402 andCNTLi 404. The ON-time and OFF-time generator 408 is coupled to feed theON-time signals TG1 and TGi to the control logic CNTL1 and CNTLirespectively. The control logic stage CNTL1 provides switching signalsSWS1 a and SWS1 b with constant ON-time pulses for switching theswitching element SW1 a and SW1 b. The control logic stage CNTLiprovides switching signals SWS1 ia and SWSib with constant ON-timepulses for switching the switching element SWia and SWib.

Issuing the next ON-time pulses is a function of the output signal 426of the compare circuit 406 and the OFF-time. The constant ON-time isgenerated in this embodiment from constant clock CLK (e.g. from acrystal oscillator). Such an implementation eases the calibrationsituation since the ON-time is nearly independent of the voltage andtemperature conditions. The primary side of the energy tracking systemis coupled to a first capacitor C1. Accordingly, one side of theswitching elements SW1 a, SWia is coupled to one side of the firstcapacitor C1. The other side of the first capacitor C1 is coupled toground. The primary side of the energy tracking system is supplied by aregulated providing power supply 206. The output or secondary side ofthe energy tracking system is coupled to a second capacitor C2 forbuffering the output voltage VO. A target board or device under test 208can be coupled to the output of the energy tracking system. The currentconsumed by the target board or device under test is the load currentIL. The level of the output voltage is VO.

One or more reference impedances 205 in the form of reference resistor Rand a switch LS can be coupled through switch LS to the energy trackingsystem. Instead of the target board the reference resistor R can beswitched to the output VO. However, the target board or DUT may still becoupled to the output during the reference measurement. The result ofthe reference measurement with the well characterized reference resistorcan then be used to calibrate the measurement for the operation with theunknown load of the target board. The energy transferred through theswitched transistor SW1, SWi during an ON-time pulse is usually muchsmaller than the stored on the capacitors C1 and C2. If the energy thatis transferred during an ON-time pulse is ESW, and the energy oncapacitor C1 is EC1, and the energy on capacitor C2 is EC2, thefollowing advantageous ratios are adventurous:ESW=k1*EC1andESW=k2*CHC2withk1 and k2>50.

ESW is much smaller than EC2 and EC1. When the output voltage VO hassettled, the compare block measures any deviation of target outputvoltage VL and versus VL(ref). The control block CNTL1 and CNTLiincrease or decrease the density of ON-time pulses. The ON-time pulsesare generated with a constant ON-time and a minimum OFF-time. Theinductors IND1 and INDi will be charged with a certain amount of energyfrom the first capacitor C1. During the OFF-time the energy in theinductors is transferred to the second capacitor C2. In an embodiment ofthe invention, the first capacitor C1 and the second capacitor C2 aresized such that this energy transfer does not significantly change thevoltages across the first capacitor C1 and the second capacitor C2.

As long as the energy in the second capacitor C2 is sufficient tomaintain the output voltage VO, the compare block will not requestanother ON-time pulse through switching signal SWS1 a, SWS1 b or SWSia,SWSib. However, if a certain load current IL is consumed by the targetboard or DUT, the voltage across the second capacitor C2 is reduceduntil the voltage compare block VL=VL(ref) determines that the outputvoltage VO at output node OUT is lower than defined and generates arequest signal to CNTL1 and CNTLi. Another ON-time pulse will then begenerated. During normal operation, this causes a pulse density ofON-time pulses of signal SWS that is proportional to the consumed energyof the DUT/target board 208. In another embodiment, the number ofON-time pulses per time counted by the accumulator and the current datathere reflects and indicates the energy consumption. Under stable inputand output voltage conditions, each ON-time pulse represents the sameamount of energy that is transferred during each ON-time pulse. TheOFF-time variations of the ON-time pulses of the switching signal SWSalso indicate current variations of the load currents IL.

A reference measurement on the known reference resistor R can be usedfor normalizing the measured current. The reference resistors R may beswitched on through switch LS in addition to the target board 208. Theinfluence of the reference resistor R on the OFF-time in signal SWSx canthen be evaluated. However, the achieved result can be improved if thereference resistors R are switched on while the target board is notconnected.

FIG. 3 shows a diagram with waveforms of the load current IL, the outputvoltage VO, and ON-time signals as applied to switches SW1 a and SWS2 a.The load current IL of the target or DUT increases at a certain point oftime. The voltage VO at the output node OUT varies according to a sawtooth scheme around the target output voltage level. The pulse densityof the ON-time pulses SWS1 a and SWS2 a increases at a certain point oftime or starts (SWS2 a) depending on the extent of the load current IL.The voltage VO varies according to a saw tooth scheme around the targetoutput voltage level (dashed line). The pulse density of the ON-timepulses increases after the load⋅current IL Increases. This change indensity of ON-time pulses of both paths is evaluated.

Although the invention has been described hereinabove with reference toa specific embodiments, It is not limited to these embodiment and nodoubt further alternatives will occur to the skilled person that liewithin the scope of the invention as claimed.

The invention claimed is:
 1. A circuit comprising: a switch having firstand second terminals, the switch's first terminal and the switch'ssecond terminal adapted to be coupled to a device under test; acapacitor having first and second terminals, the capacitor's firstterminal coupled to the switch's first terminal and the capacitor'ssecond terminal coupled to the switch's second terminal; an inductorhaving first and second terminals, the inductor's first terminal iscoupled to the capacitor's first terminal; a transistor having a controlterminal, a first channel terminal, and a second channel terminal, thetransistor's first channel terminal coupled to the inductor's secondterminal and the transistor's second terminal is coupled to the switch'ssecond terminal.
 2. The circuit of claim 1, further comprising a controlcircuit that is coupled to the transistor's control terminal, thecontrol circuit comprises: an ON-time generator; a control logic blockcoupled to the on-time generator and configured to generate signals forthe transistor's control terminal, the signals having ON-time pulses;and an accumulator coupled to the control logic block and configured tocollect the number of ON-time pulses.
 3. The circuit of claim 1, furthercomprising a resistor coupled between the switch's first terminal andthe capacitor's first terminal.
 4. The circuit of claim 1, furthercomprising a diode having an anode terminal and a cathode terminal, thediode's anode terminal coupled to the transistor's second terminal andthe diode's cathode terminal coupled to the transistor's first terminal.5. The circuit of claim 1, further comprising a second switch having acontrol terminal, a first channel terminal, and a second channelterminal, the second switch's first channel terminal is coupled to theinductor's second terminal and the second switch's second terminal isadapted to be coupled to an input voltage source.
 6. The circuit ofclaim 4, wherein the second transistor's control terminal is adapted tobe coupled to a control circuit.
 7. The circuit of claim 1, where thetransistor's control terminal is adapted to be coupled to a controlcircuit.
 8. The circuit of claim 1, wherein the transistor's secondchannel terminal is adapted to be coupled to a power supply.
 9. Thecircuit of claim 1, wherein the capacitor's first terminal is adapted tobe coupled to a power supply.